In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Arrangements which include first and second relatively movable members have traditionally posed a number of different engineering problems to be resolved. One such challenge involves dealing with the friction which occurs at the interface between first and second relatively movable members. Another challenge involves dealing with corrosion, which can be caused by exposure to a harsh environment and/or mechanical wear.
One such arrangement is a bearing disposed between concentric relatively movable members, such as a shaft and housing. Such bearings are utilized in a number of different types of applications and machinery. For example, a typical marine propulsion system includes such a bearing arrangement at a joint which is designed to permit pivotable movement of a drive shaft. This pivotable joint is typically referred to as a gimbal, and the bearing associated therewith is referred to as a gimbal bearing.
A number of problems and disadvantages have been associated with conventional gimbal bearing design. Typically, a rubber bellows surrounds the gimbal bearing assembly, which includes a bearing housing ring and a rolling bearing disposed concentrically therein. The bellows is intended to shield the bearing assembly from the harmful effects of exposure to the surrounding marine environment. However, these rubber bellows are prone to failure resulting in exposure of the bearing assembly to the marine environment and in corrosion of the assembly.
The housing ring of the bearing assembly is typically formed from an aluminum alloy having a high hardness. This material is selected to resist corrosion caused by exposure to a marine environment, as well as fretting corrosion caused by the load bearing contact between the inner bore of the housing ring and the outer race of the bearing. However, such housing rings are prone to bind with the outer race of the bearing ring. This binding can make removal and/or installation of the bearing within the housing ring extremely difficult.
As alluded to above, the bearing is provided concentrically within the housing ring with an interference fit resulting in a torque value at the joint of approximately 15-60 ft.-lbs. This relatively tight interference fit is provided in order to prevent looseness between the housing ring and a bearing disposed therein. However, this interference fit makes installation and removal of the bearing difficult, necessitating the use of special tools and techniques for successfully completing installation and/or removal of the gimbal bearing.
Conventional gimbal bearings often use shield plates between the inner and outer races thereof in order to prevent escape of lubricant contained within the bearing. These shield plates act as non-contacting seals. Non-contacting seals are preferred to prevent fretting on the outer surface of the inner race. Thus, a small gap remains between the end of the shield plate and the surface of the inner race of the bearing. This small gap provides an opportunity for escape of the lubricant contained within the bearing. Thus, these bearing assemblies are typically provided with a port in the outer race of the bearing which allows for the introduction of lubricant to replace any lubricant lost from within the bearing. These ports must be machined in the steel bearing rings, or otherwise provided during manufacture. Providing this feature represents an added manufacturing cost. The necessity of relubricating the bearing represents a maintenance cost, as well as an inconvenience. Moreover, the lubrication port of the bearing ring must be properly aligned with a mechanism, such as another port or groove, disposed in the surrounding housing ring in or to allow for the introduction of lubricant. This required alignment complicates the replacement/installation of the bearing within the surrounding housing ring.
Thus, a need exists for an improved arrangement which comprises relatively movable members, such as a gimbal bearing assembly including a housing ring and bearing disposed concentrically therein.